New information on beta-delayed neutron emission from Be-12,Be-14

The beta-delayed neutron branches from neutron-rich Be-isotopes have been m easured with a setup sensitive down to thermal energies. For Be-14 a new va lue of P-n = 101 +/- 4% has been found for the total neutron-emission proba bility and an upper limit of 2.4% (95% confidence level) is imposed on the combination P-2n + 3P(3n) of multi-neutron emission probabilities. Moreover , an improved value of P-n = 0.50 +/- 0.03% has been obtained for Be-12. A time-correlation method, previously developed for a continuous radioactive beam to determine neutron branching ratios, has been revised and adapted to the pulsed secondary beam at ISOLDE, CERN. (C) 1999 Elsevier Science B.V. All rights reserved.